To get vibration characteristics over 23 wards in Tokyo, measurements of “S” and “P” wave velosities were taken at 8 places. From these measurements, more considerable scattering in “S” wave velosities are observed in sandy layers, and gravel and sand layers comparing with clay Formation. And also, as for the “S” wave velosities of upper Yurakucho Layers, we found that N-Value is separated into 2 groups by the values of “N=O” and “N≥1”. The density of subsoil measured in the field using scattering γ-ray is coincided with the density obtained in our laboratory test.
It is possible that the “Kazusa-Group” is one of the strongest seismic baserocks in Tokyo. It was found that the “Kazusa-Group” is thick, for instance, in the Edogawa area, it is over 2, 000m and in the Tama area, over 500m. It means that the layer is physically fixed by referring the resistivity test by electrical logging and the densities of subsoil measured with γ-ray.
“S” wave velosities in the Kazusa-Group measured in Denenchofu area, one of the 8 places, are 580m/s in the field test, and by ultrasonic 650m/s.